Low-Pressure H2, NH3 Microwave Plasma Treatment of Polytetrafluoroethylene (PTFE) Powders: Chemical, Thermal and Wettability Analysis

• Main Authors: Harald Hunke, Navneet Soin, Tahir H. Shah, Erich Kramer, Alfons Pascual, Mallampalli Sri Lakshmi Karuna, Elias Siores
• Format: Article
• Language: English
• Published: MDPI AG 2015-04-01
• Series: Materials
• Subjects: polytetrafluoroethylene (PTFE); low-pressure microwave plasma; ESCA/XPS; degeneration; thermal stability
• Online Access: http://www.mdpi.com/1996-1944/8/5/2258

Functionalization of Polytetrafluoroethylene (PTFE) powders of ~6 μm particle size is carried out using low-pressure 2.45 GHz H2, NH3 microwave plasmas for various durations (2.5, 10 h) to chemically modify their surface and alter their surface energy. The X-ray Photoelectron Spectroscopy (XPS) analyses reveal that plasma treatment leads to significant defluorination (F/C atomic ratio of 1.13 and 1.30 for 10 h NH3 and H2 plasma treatments, respectively vs. 1.86 for pristine PTFE), along with the incorporation of functional polar moieties on the surface, resulting in enhanced wettability. Analysis of temperature dependent XPS revealed a loss of surface moieties above 200 °C, however, the functional groups are not completely removable even at higher temperatures (>300 °C), thus enabling the use of plasma treated PTFE powders as potential tribological fillers in high temperature engineering polymers. Ageing studies carried over a period of 12 months revealed that while the surface changes degenerate over time, again, they are not completely reversible. These functionalised PTFE powders can be further used for applications into smart, high performance materials such as tribological fillers for engineering polymers and bio-medical, bio-material applications.